The UN World Food Programme (WFP) estimates 175,000 people are without food, water and electricity and in need of help.

"The floodwaters were so strong in Gonaives that they have washed away the whole town," WFP Country Director Guy Gauvreau told BBC News Online.

"People don't have the means to cook, and they lack water."

"We could have had an earthquake or a civil war but this is worse because it has washed everything away," he said.

In the past year Haiti has faced a series of crises including armed revolts, military intervention and deadly floods.

Aid difficult

Aid efforts led by international agencies are under way, assisted by 3,000 UN peacekeeping troops already in the country.

But severed road links and a tense security situation are hampering efforts.

The WFP said aid trucks carrying emergency food supplies had been lined up to form a makeshift bridge over the water.

The International Red Cross said it was considering the use of boats to reach trapped people.

The EU announced it would send 1.5m euros ($1.8m) in urgent aid, and the US Embassy offered $60,000 in immediate relief.

NORTHERN HAITI UNDER WATER

1. The island of La Tortue was barely visible but Haitian officials now say nothing happened there.2. About 30% of Port-de-Paix city is reported to be covered by water along the coast and nearby plantations are reported to be under water. The road to Gonaives is flooded.3. The water level of the river is reported to be very high and some villages on its banks have been flooded.4. Flooding has hit all urban areas of Gonaives, affecting about 175,000 people - some 600 people are believed to have died there.